Bump spec_tests/hed-specification from 23dfb19 to a9bf8b5

Bumps [spec_tests/hed-specification](https://github.com/hed-standard/hed-specification) from `23dfb19` to `a9bf8b5`.
- [Release notes](https://github.com/hed-standard/hed-specification/releases)
- [Commits](hed-standard/hed-specification@23dfb19...a9bf8b5)

---
updated-dependencies:
- dependency-name: spec_tests/hed-specification
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>